Article
pubs.acs.org/jced
Densities and Viscosities of Mixtures of Two Ionic Liquids Containing
a Common Cation
Hugo F. D. Almeida,†,‡ José N. Canongia Lopes,†,§ Luís P. N. Rebelo,† Joaõ A. P. Coutinho,‡
Mara G. Freire,‡ and Isabel M. Marrucho*,†,§
†
Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal
CICECOInstituto de Materiais de Aveiro, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal
§
Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
‡
S Supporting Information
*
ABSTRACT: Density and dynamic viscosity data of binary
mixtures of ionic liquids (ILs) were determined in this work,
at temperatures from 283.15 to 363.15 K and at 0.1 MPa. The
mixtures of two ILs comprise a common cation and different
anions, combining 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with eight other ionic liquids,
namely, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium
tricyanomethane, 1-butyl-3-methylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium dimethylphosphate. Five mole fractions (0.00, 0.25, 0.50, 0.75, 1.00) of
each mixture were prepared and characterized in terms of density and dynamic viscosity. The temperature dependence of density
was described using a linear model, while the Vogel−Tammann−Fulcher equation was used to describe the temperature
dependence of viscosity. Ideal mixing rules were used to predict the molar volume and viscosity and to infer on the mixtures
ideal/nonideal behavior. For the mixtures of ILs investigated almost null or small deviations were observed in the molar volumes,
meaning that their mixing is remarkably close to linear ideal behavior when molar volumes of mixtures are considered. For
viscosity, larger deviations were observed for some particular systems; yet, and in general, mixtures of ILs do not deviate in a
significant extent from ideal behavior. Therefore, ideal mixture models can be used to predict the physical properties of mixtures
of ILs and to a priori design mixtures with specific features.
■
INTRODUCTION
Ionic liquids (ILs), known as salts with a melting temperature
below a conventional temperature of 100 °C,1 have been largely
explored in the past few years and are at last start reaching their
place in industry.2 Ionic liquids are typically composed of an
organic cation and an organic or inorganic anion, where a large
number of potential fluids can be synthesized by simple chemical
structural rearrangements either in the cation or in the anion.
In an ideal situation, the combination of different ions allocates
the tailoring of their properties and characteristics and allows
them to be task specific fluids for particular applications. The
ionic nature and the large array of cation−anion combinations of
ILs are the main characteristics responsible for some of their outstanding properties, namely, a negligible vapor pressure, a high
ionic conductivity, nonflammability, high thermal and chemical
stabilities, and an enhanced solvation ability for a large variety of
compounds.2−8 Due to the great interest in ILs from fundamental and applied point of views, and the wide number of ILs
that is possible to obtain by the simple combination of the available cations and anions, the study of thermophysical properties
© 2016 American Chemical Society
of ILs mixtures is an important task given that the possibility of
finding tailored fluids with target properties is largely increased.
Recently, Niedermeyer et al.9 reported a critical review on the
use of mixtures of two and three ILs as a way of further extending
the ability to design ILs with tailored properties.9,10 The authors9
proposed a nomenclature for such mixtures, and here adopted,
where mixtures of two ILs, [A][X] and [A][Y], bearing a
common cation [A]+, is abbreviated to [A][X]x[Y](1−x), whereas
for the [A][X] + [B][X] mixtures, bearing a common anion
[X]−, it is abbreviated to [A]x[B](1−x), [X], where x and (1 − x)
are the mole fraction of each IL.9 Within IL mixtures, Canongia
Lopes et al.10 provided a pioneering work on their excess molar
volumes (VE), namely for the following mixtures: [C4C1im][PF6]x[NTf2](1−x), [C4C1im][BF4]x[NTf2](1−x), and [C4C1im][BF4]x[PF6](1−x). All of these mixtures were found to exhibit
Special Issue: In Honor of Kenneth R. Hall
Received: February 29, 2016
Accepted: July 4, 2016
Published: July 14, 2016
2828
DOI: 10.1021/acs.jced.6b00178
J. Chem. Eng. Data 2016, 61, 2828−2843
Journal of Chemical & Engineering Data
Article
mixtures with [C4C1im][NTf2]: (i) ILs containing fluorinated
anions, such as [C4C1im][BF4], [C4C1im][PF6], and [C4C1im][CF3SO3]; (ii) ILs containing cyano-based anions, [C4C1im][SCN], [C4C1im][N(CN)2], and [C4C1im][C(CN)3]; and (iii)
ILs containing nonfluorinated organic acids derived anions, such
as [C4C1im][CH3CO2] and [C4C1im][(CH3O)2PO2]. Densities
and dynamic viscosities of eight mixtures of two ILs were studied
in this paper, namely, [C4C1im][NTf2]x[SCN](1−x), [C4C1im][NTf 2 ] x [N(CN) 2 ] (1−x) , [C 4 C 1 im][NTf 2 ] x [C(CN) 3 ] (1−x) ,
[C 4 C 1 im][NTf 2 ] x [BF 4 ] (1−x) , [C 4 C 1 im][NTf 2 ] x [PF 6 ] (1−x) ,
[C 4 C 1 im][NTf 2 ] x [CH 3 CO 2 ] ( 1 − x ) , [C 4 C 1 im][NTf 2 ] x [CF3SO3](1−x), and [C4C1im][NTf2]x[(CH3O)2PO2](1−x), at
temperatures between 283.15 and 363.15 K and at 0.1 MPa.
Five mole fractions of [C4C1im][NTf2] were investigated for
each mixture (x = 0.00, 0.25, 0.50, 0.75, and 1.00), which include
the respective properties for the pure ILs.
almost linear mixing behavior. Excess molar volumes for these
mixtures were always found to be smallless than 0.1% of the
overall volume and less than 1.5% of the difference in the molar
volumes of the pure components. Similar results were presented
by Clough et al.,11 where the VE for an extended number of
mixtures presents deviations lower than 0.5%. Density measurements by Stoppa et al.12 and Larriba et al.13 showed that the
excess molar volumes for [C2C1im][N(CN)2]x[BF4](1−x) and
[C4C1pyrr][BF4]x[NTf2](1−x), respectively, are small and
positive (0.1%), in agreement with the results of Canongia
Lopes et al.10 for [C4C1im][BF4]x[PF6](1−x). Larriba et al.13 also
determined refractive indices, densities, and viscosities of a mixture
of two pyridinium-based ILs, namely, [C4py][BF4]x[NTf2](1−x).
Gouveia et al.14 determined the density, viscosity, and refractive
index of mixed imidazolium-based ILs, containing a common
cation and the tricyanomethane anion, combined with a series of
amino acid based fluids, namely, [C2C1im][C(CN)3]x[Gly](1−x),
[C 2 C 1 im][C(CN) 3 ] x [ L -Ala] (1−x) , [C 2 C 1 im][C(CN) 3 ] x [Tau](1−x), [C2C1im][C(CN)3]x[L-Ser](1−x), and [C2C1im][C(CN)3]x[L-Pro](1−x).
In addition to the previous studies where mixtures of ILs with a
common cation were investigated, further studies appeared on
mixtures composed of ILs with the same anion and cation
core, yet changing the cation alkyl side chain length.8,15,16 Navia
et al.8,15 determined densities, excess molar volumes, isobaric
thermal expansivities, excess enthalpies, and viscosities of
[C6C1im]x[C2C1im](1−x)[BF4], [C6C1im]x[C4C1im](1−x) [BF4],
[C4C1im][BF4]x[MeSO4](1−x), and [C4C1im][BF4]x[PF6](1−x).
Song and Chen16 determined viscosities and densities of
[C2C1im]x[C3C1im](1−x)[BF4], [C3C1im]x[C6C1im](1−x)[BF4],
and [C2C1im]x[C6C1im](1−x)[BF4]. On the other hand, analyses
of mixtures of two ILs bearing distinct cation cores, like
pyrrolidinium and pyridinium, as well as with different anions,
were performed. Viscosity and NMR-based data on ion−ion
correlations and diffusion of pyrrolidinium- and imidazoliumbased ionic liquids were measured by Castiglione et al.17 for
[C1C4pyr][NTf2]x[BETI](1−x), [C1C4pyr][NTf2]x[IM14](1−x),
[C 1 C 4 pyr][BETI] x [IM 14 ] (1−x) , and [C 1 C 4 pyr][NTf 2 ] x [BETI]y[IM14](1−x−y).
The aim of this work consists on the determination and
analysis of densities and dynamic viscosities of mixtures of two
ILs containing the common 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C4C1im][NTf2], mixed with an
additional IL also based on the 1-butyl-3-methylimidazolium
cation, yet with different anions. The [C4C1im][NTf2] IL was
chosen as a starting point of this study since it is a well-studied IL,
with accurate density and dynamic viscosity data available.18−25
Members of three different families of ILs, with different properties regarding density and viscosity, were chosen to prepare
■
EXPERIMENTAL SECTION
Materials. Binary IL mixtures were prepared with 1-butyl-3methylimidazolium bis(trifluoromethylsulfonyl)imide
([C4C1im][NTf2]), combined with 1-butyl-3-methylimidazolium
thiocyanate ([C4C1im][SCN]), 1-butyl-3-methylimidazolium
dicyanamide ([C4C1im][N(CN)2]), 1-butyl-3-methylimidazolium tricyanomethane ([C4C1im][C(CN)3]), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4C1im][BF4]), 1-butyl-3methylimidazolium hexafluorophosphate ([C4C1im][PF6]),
1-butyl-3-methylimidazolium acetate ([C4C1im][CH3CO2]),
1-butyl-3-methylimidazolium trifluoromethanesulfonate
([C4C1im][CF3SO3]), and 1-butyl-3-methylimidazolium dimethylphosphate ([C4C1im][(CH3O)2PO2]). In Table 1 are listed
the ILs used in this work, along with the CAS number, purity, and
source. Furthermore, the purity of each IL, after the drying step
described below, was further checked by 1H and 13C NMR (and
19
F NMR for the fluorinated ILs).
Preparation of Ionic Liquid Mixtures. Before the
preparation of each mixture, pure ILs were dried at moderate
temperature (≈ 318 K) and high vacuum (≈ 10−5 Pa), under
constant stirring, for a minimum period of 48 h, to remove traces
of water and volatile compounds. Binary mixtures of ILs were
then prepared using an analytical balance (model Mettler Toledo
XS205 Dual Range) with an accuracy of 4 × 10−6 g. To ensure a
proper mixing, magnetic stirring for at least 20 min, in closed gall
vials, was carried out. Afterward, the prepared binary mixtures of
ILs at 0.25, 0.50, and 0.75 mole fractions of [C4mim][NTf2] were
dried again at moderate temperature (≈ 318 K) and high vacuum
(≈ 10−5 Pa), under constant stirring, for a minimum period of 48 h.
After the drying step and immediately before the measurements of
density and viscosity, the water content of each pure and mixture of
ILs was determined by Karl Fischer titration, making use of a
Table 1. Specifications of the Compounds Used
compound
abbreviation
CAS No.
source
initial mole
fraction purity
purification
procedures
1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
1-butyl-3-methylimidazolium thiocyanate
1-butyl-3-methylimidazolium dicyanamide
1-butyl-3-methylimidazolium tricyanomethane
1-butyl-3-methylimidazolium tetrafluoroborate
1-butyl-3-methylimidazolium hexafluorophosphate
1-butyl-3-methylimidazolium acetate
1-butyl-3-methylimidazolium trifluoromethanesulfonate
1-butyl-3-methylimidazolium dimethylphosphate
[C4C1im][NTf2]
[C4C1im][SCN]
[C4C1im][N(CN)2]
[C4C1im][C(CN)3]
[C4C1im][BF4]
[C4C1im][PF6]
[C4C1im][CH3CO2]
[C4C1im][CF3SO3]
[C4C1im][(CH3O)2PO2]
174899-83-3
344790-87-0
448245-52-1
878027-73-7
174501-65-6
174501-64-5
284049-75-8
174899-66-2
891772-94-4
Iolitec
Iolitec
Iolitec
Merck
Iolitec
Iolitec
Iolitec
Iolitec
Iolitec
0.99
>0.98
>0.98
>0.98
0.99
0.99
0.98
0.99
>0.98
drying
drying
drying
drying
drying
drying
drying
drying
drying
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J. Chem. Eng. Data 2016, 61, 2828−2843
Journal of Chemical & Engineering Data
Article
presented in Table 2. ILs from three different families of anions
were selected to prepare binary mixtures with [C4C1im][NTf2].
From the results obtained, it is possible to drawn general trends
for each one of the different families: (i) ILs containing cyanobased anions are generally the most fluid and the least dense, due
most likely to the fact that both anion charge density and anion
mass density are low;29 (ii) ILs with fluorine-containing anions
have intermediate viscosity (with exception of highly viscous
[C4C1im][PF6]) and are quite dense (with the exception of
[C4C1im][BF4] due to low charge density and low symmetry of
the anion),29 owing to the presence of the fluorine atoms that
increase density and their noncoordinating nature resulting in low
viscous fluids; and (iii) ILs bearing nonfluorinated and organic
acids derived anions are the most viscous, due to the high hydrogen
bonding ability of these anions, and have intermediate density.
Volumetric Properties. The density values of pure and
binary mixtures of ILs were determined at 0.1 MPa in the
temperature range from 283.15 to 363.15 K and 0.1 MPa. The
results obtained are presented in Table 3. The relative deviations
between the data measured in this work and those already
reported18−22,24,26,30−40 for the pure ILs were also determined
and are depicted in Figure S1. These relative deviations, between
different authors and for different ILs, range from −0.65% up
Metrohm 831 Karl Fischer coulometer. The reagent employed was
Hydranal-Coulomat AG from Riedel-de Haën. The water content
of each IL and mixture is presented in Table 2.
Density and Viscosity Measurements. Density (ρ) and
dynamic viscosity (η) measurements were carried out using an
automated SVM 300 Anton Paar rotational Stabinger
viscometer−densimeter in the temperature range from 283.15
to 363.15 K, at 0.1 MPa. The absolute uncertainty in density
is ±0.0005 g·cm−3, and the relative uncertainty in dynamic
viscosity is ±0.35% according to the manufacturer. The relative
uncertainty in temperature is within ±0.02 K. Further details on
the use of the same equipment for the determination of viscosities
and densities of ILs can be found elsewhere.26−28 The measured
viscosity and density and the calculated molar volume, Vm, of the
pure ILs and their mixture at 298.15 K are presented in Table 2.
■
RESULTS AND DISCUSSION
In Table 2, the water content of the pure ILs and studied mixtures
of ILs is presented. It can be observed that these values are rather
small, ranging from 0.0089% up to 0.0986% in mass, even for the
most hydrophilic ILs, such as [C4C1im][CH3CO2]. Also, a
summary of the viscosity, density, and molar volume for all the
studied mixtures and pure fluids at 298.15 K and 0.1 MPa is
Table 2. Composition, Water Content, Viscosity (η), Density (ρ), and Calculated Molar Volume (Vm) for the Studied Binary
Mixtures at 298.15 K and 0.1 MPaa
composition/mole fraction
x ([C4C1im][NTf2])
[C4C1im][NTf2]
[C4C1im][SCN]
[C4C1im][N(CN)2]
[C4C1im][C(CN)3]
[C4C1im][BF4]
[C4C1im][PF6]
[C4C1im][CF3SO3]
[C4C1im][CH3CO2]
[C4C1im][(CH3O)2PO2]
[C4C1im][NTf2]0.25[SCN]0.75
[C4C1im][NTf2]0.50[SCN]0.50
[C4C1im][NTf2]0.75[SCN]0.25
[C4C1im][NTf2]0.25[N(CN)2]0.75
[C4C1im][NTf2]0.50[N(CN)2]0.50
[C4C1im][NTf2]0.75[N(CN)2]0.25
[C4C1im][NTf2]0.25[C(CN)3]0.75
[C4C1im][NTf2]0.50[C(CN)3]0.50
[C4C1im][NTf2]0.75[C(CN)3]0.25
[C4C1im][NTf2]0.25[BF4]0.75
[C4C1im][NTf2]0.50[BF4]0.50
[C4C1im][NTf2]0.75[BF4]0.25
[C4C1im][NTf2]0.25[PF6]0.75
[C4C1im][NTf2]0.75[PF6]0.25
[C4C1im][NTf2]0.50[PF6]0.50
[C4C1im][NTf2]0.25[CF3SO3]0.75
[C4C1im][NTf2]0.50[CF3SO3]0.50
[C4C1im][NTf2]0.75[CF3SO3]0.25
[C4C1im][NTf2]0.25[CH3CO2]0.75
[C4C1im][NTf2]0.50[CH3CO2]0.50
[C4C1im][NTf2]0.75[CH3CO2]0.25
[C4C1im][NTf2]0.25[(CH3O)2PO2]0.75
[C4C1im][NTf2]0.50[(CH3O)2PO2]0.50
[C4C1im][NTf2]0.75[(CH3O)2PO2]0.25
1.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.2501
0.4999
0.7483
0.2506
0.4569
0.7486
0.2517
0.5000
0.7508
0.2497
0.4979
0.7509
0.2499
0.7479
0.4996
0.2503
0.5001
0.7460
0.2498
0.4984
0.7487
0.2499
0.5005
0.7468
(1 − x) ([C4C1im][Y]) water content (% mass) M (g·mol−1) η (mPa·s) ρ (g·cm−3) Vm (cm3·mol−1)
0.0000
1.0000
1.0000
1.0000
1.0000
1.0000
1.0000
1.0000
1.0000
0.7499
0.5001
0.2517
0.7494
0.5431
0.2514
0.7483
0.5000
0.2492
0.7503
0.5021
0.2491
0.7501
0.2521
0.5004
0.7497
0.4999
0.2540
0.7502
0.5016
0.2513
0.7501
0.4995
0.2532
0.0089
0.0220
0.0243
0.0216
0.0780
0.0332
0.0341
0.0467
0.0165
0.0140
0.0275
0.0199
0.0192
0.0138
0.0164
0.0106
0.0214
0.0627
0.0488
0.0263
0.0563
0.0194
0.0168
0.0222
0.0346
0.0405
0.0399
0.0986
0.0863
0.0658
0.0475
0.0202
0.0200
419.37
197.30
205.26
229.28
226.02
287.18
288.29
198.26
264.03
252.82
308.34
363.85
258.79
312.32
365.84
276.80
324.33
371.85
274.36
322.70
371.03
320.23
386.32
353.28
321.06
353.83
386.60
253.54
308.82
364.09
302.87
341.70
380.54
51.58
62.64
30.08
27.97
108.74
285.02
99.14
292.57
641.71
61.69
58.50
55.06
36.45
41.02
46.82
31.92
37.61
43.15
88.56
72.77
60.64
148.96
68.88
97.74
71.42
66.62
68.68
189.58
119.72
76.32
432.55
222.26
104.86
1.4372
1.0702
1.0602
1.0476
1.2016
1.3676
1.2963
1.0528
1.1579
1.1954
1.2931
1.3717
1.1830
1.2685
1.3681
1.1672
1.2688
1.3581
1.2791
1.3428
1.3951
1.3894
1.4237
1.4080
1.3398
1.3755
1.4078
1.1819
1.2838
1.3678
1.2391
1.3120
1.3770
291.80
184.36
193.60
218.86
188.10
209.99
222.39
188.32
228.03
246.34
281.37
295.54
252.77
284.77
296.70
267.89
293.07
300.07
242.80
276.16
291.97
248.31
288.71
274.36
258.00
281.07
291.98
249.57
283.47
296.45
267.92
290.07
297.41
Standard uncertainties u are u(x,y) = 0.0001, u(T) = 0.02 K, u(p) = 10 kPa, the combined expanded uncertainty Uc is Uc(ρ) = 0.5 kg·m−3, and
expanded uncertainty Ur is Ur(η) = 0.05, with an expanded uncertainty at the 0.95 confidence level (k ≈ 2).
a
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Journal of Chemical & Engineering Data
Article
Table 3. Experimental Densities (ρ) of the Studied Mixtures of Ionic Liquids as a Function of Temperature (T) at Pressure
p = 0.1 MPaa
x [C4C1im][NTf2] + (1 − x) [C4C1im][SCN]
x [C4C1im][NTf2] + (1 − x) [C4C1im][N(CN)2]
ρ (g·cm−3)
ρ (g·cm−3)
x
x
T (K)
1.000
0.250
0.000
T (K)
1.000
0.251
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.3853
1.3053
1.2062
1.4469
1.3807
1.3012
1.2026
1.4421
1.3762
1.2971
1.1990
1.4372
1.3717
1.2931
1.1954
1.4324
1.3673
1.289
1.1918
1.4276
1.3628
1.285
1.1883
1.4229
1.3584
1.281
1.1847
1.4182
1.3540
1.2771
1.1812
1.4135
1.3497
1.2731
1.1777
1.4088
1.3453
1.2692
1.1743
1.4041
1.3410
1.2653
1.1708
1.3994
1.3367
1.2615
1.1674
1.3948
1.3324
1.2576
1.1640
1.3902
1.3281
1.2538
1.1606
1.3856
1.3239
1.2500
1.1573
1.3811
1.3197
1.2462
1.1540
1.3766
1.3155
1.2424
1.1507
x [C4C1im][NTf2] + (1 − x) [C4C1im][C(CN)3]
1.0792
1.0762
1.0732
1.0702
1.0672
1.0642
1.0613
1.0584
1.0555
1.0526
1.0498
1.0470
1.0441
1.0414
1.0386
1.0358
1.0331
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.3818
1.2808
1.1943
1.4469
1.3772
1.2766
1.1905
1.4421
1.3727
1.2725
1.1867
1.4372
1.3681
1.2685
1.1830
1.4324
1.3636
1.2644
1.1793
1.4276
1.3592
1.2604
1.1757
1.4228
1.3547
1.2564
1.1720
1.4181
1.3503
1.2524
1.1684
1.4134
1.3459
1.2485
1.1649
1.4087
1.3415
1.2446
1.1613
1.4040
1.3372
1.2407
1.1578
1.3993
1.3329
1.2368
1.1543
1.3947
1.3286
1.233
1.1508
1.3901
1.3243
1.2292
1.1473
1.3855
1.3200
1.2254
1.1438
1.3810
1.3158
1.2216
1.1404
1.3764
1.3116
1.2179
1.1370
x [C4C1im][NTf2] + (1 − x) [C4C1im][BF4]
1.0700
1.0667
1.0634
1.0602
1.0570
1.0538
1.0506
1.0475
1.0444
1.0413
1.0382
1.0352
1.0321
1.0291
1.0261
1.0232
1.0203
0.748
0.500
0.749
0.457
ρ (g·cm−3)
ρ (g·cm−3)
x
x
T (K)
1.000
0.252
0.000
T (K)
1.000
0.250
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.3719
1.2816
1.1789
1.4469
1.3673
1.2773
1.175
1.4421
1.3627
1.2730
1.1711
1.4372
1.3581
1.2688
1.1672
1.4324
1.3536
1.2646
1.1634
1.4276
1.3491
1.2604
1.1596
1.4228
1.3446
1.2563
1.1558
1.4181
1.3402
1.2522
1.1521
1.4134
1.3358
1.2481
1.1483
1.4087
1.3314
1.2440
1.1446
1.4040
1.3270
1.2400
1.1409
1.3993
1.3227
1.2359
1.1373
1.3947
1.3184
1.2320
1.1337
1.3901
1.3141
1.228
1.1300
1.3855
1.3098
1.2241
1.1265
1.381
1.3056
1.2202
1.1229
1.3764
1.3014
1.2163
1.1194
x [C4C1im][NTf2] + (1 − x) [C4C1im][PF6]
1.0581
1.0546
1.0511
1.0476
1.0442
1.0408
1.0375
1.0341
1.0308
1.0275
1.0242
1.0209
1.0177
1.0145
1.0113
1.0081
1.0050
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.4091
1.3558
1.2912
1.4469
1.4044
1.3514
1.2871
1.4421
1.3998
1.3471
1.2831
1.4372
1.3951
1.3428
1.2791
1.4324
1.3905
1.3385
1.2751
1.4276
1.3860
1.3342
1.2712
1.4228
1.3815
1.3299
1.2673
1.4181
1.3769
1.3257
1.2634
1.4134
1.3724
1.3214
1.2595
1.4087
1.3680
1.3172
1.2556
1.4040
1.3635
1.3131
1.2518
1.3993
1.3591
1.3089
1.248
1.3947
1.3548
1.3048
1.2442
1.3901
1.3504
1.3007
1.2404
1.3855
1.346
1.2966
1.2367
1.381
1.3417
1.2926
1.233
1.3764
1.3375
1.2886
1.2293
x [C4C1im][NTf2] + (1 − x) [C4C1im][CH3CO2]
1.2125
1.2088
1.2052
1.2016
1.1980
1.1945
1.1909
1.1874
1.1840
1.1805
1.1770
1.1736
1.1702
1.1668
1.1634
1.1601
1.1568
0.751
0.501
0.751
ρ (g·cm−3)
0.498
ρ (g·cm−3)
x
x
T (K)
1.000
0.748
0.500
0.250
0.000
T (K)
1.000
0.749
0.498
0.250
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
1.4518
1.4469
1.4421
1.4372
1.4324
1.4276
1.4228
1.4181
1.4134
1.4087
1.4040
1.3993
1.3947
1.3901
1.4374
1.4331
1.4284
1.4237
1.4190
1.4143
1.4097
1.4051
1.4005
1.3959
1.3913
1.3868
1.3823
1.3779
1.4211
1.4172
1.4126
1.4080
1.4035
1.399
1.3945
1.3900
1.3856
1.3812
1.3767
1.3723
1.3680
1.3636
1.4025
1.3983
1.3938
1.3894
1.3850
1.3807
1.3764
1.3721
1.3679
1.3636
1.3594
1.3552
1.3510
1.3469
1.3799
1.3765
1.3720
1.3676
1.3634
1.3592
1.3551
1.3510
1.3470
1.3429
1.3389
1.3349
1.3309
1.3269
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
1.4518
1.4469
1.4421
1.4372
1.4324
1.4276
1.4229
1.4182
1.4135
1.4088
1.4041
1.3994
1.3948
1.3902
1.3814
1.3768
1.3723
1.3678
1.3633
1.3588
1.3543
1.3499
1.3454
1.3410
1.3366
1.3323
1.3279
1.3236
1.2965
1.2922
1.2880
1.2838
1.2797
1.2757
1.2716
1.2675
1.2635
1.2594
1.2554
1.2514
1.2475
1.2435
1.1932
1.1894
1.1856
1.1819
1.1783
1.1747
1.1711
1.1675
1.1639
1.1603
1.1568
1.1532
1.1497
1.1461
1.0627
1.0594
1.0560
1.0528
1.0497
1.0466
1.0435
1.0405
1.0375
1.0345
1.0315
1.0285
1.0256
1.0226
2831
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Journal of Chemical & Engineering Data
Article
Table 3. continued
x [C4C1im][NTf2] + (1 − x) [C4C1im][PF6]
T (K)
1.000
353.15
358.15
363.15
1.3855
1.3734
1.3810
1.369
1.3764
1.3646
x [C4C1im][NTf2] + (1 −
0.748
x [C4C1im][NTf2] + (1 − x) [C4C1im][CH3CO2]
ρ (g·cm−3)
ρ (g·cm−3)
x
x
0.250
0.000
T (K)
1.3593
1.3427
1.3551
1.3386
1.3508
1.3346
x) [C4C1im][CF3SO3]
1.3230
1.3190
1.3152
353.15
358.15
363.15
0.500
1.000
0.749
0.498
1.3856
1.3194
1.3811
1.3151
1.3766
1.3109
x [C4C1im][NTf2] + (1 − x)
ρ (g·cm−3)
0.250
1.2396
1.1426
1.2357
1.1391
1.2318
1.1356
[C4C1im][(CH3O)2PO2]
0.000
1.0197
1.0167
1.0139
ρ (g·cm−3)
x
x
T (K)
1.000
0.746
0.500
0.250
0.000
T (K)
1.000
0.747
0.501
0.250
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.4469
1.4421
1.4372
1.4324
1.4276
1.4229
1.4182
1.4135
1.4088
1.4041
1.3994
1.3948
1.3902
1.3856
1.3811
1.3766
1.4218
1.4171
1.4124
1.4078
1.4032
1.3986
1.3940
1.3894
1.3849
1.3804
1.3760
1.3715
1.3671
1.3626
1.3582
1.3538
1.3495
1.3890
1.3844
1.3799
1.3755
1.3710
1.3666
1.3622
1.3578
1.3535
1.3492
1.3449
1.3406
1.3363
1.3320
1.3278
1.3235
1.3193
1.3527
1.3483
1.3440
1.3398
1.3355
1.3313
1.3270
1.3228
1.3187
1.3145
1.3104
1.3062
1.3022
1.2981
1.2940
1.2900
1.2861
1.3084
1.3043
1.3003
1.2963
1.2923
1.2884
1.2845
1.2806
1.2767
1.2728
1.2689
1.2651
1.2613
1.2575
1.2537
1.2499
1.2462
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.4518
1.4469
1.4421
1.4372
1.4324
1.4276
1.4229
1.4182
1.4135
1.4088
1.4041
1.3994
1.3948
1.3902
1.3856
1.3811
1.3766
1.3906
1.3860
1.3815
1.3770
1.3725
1.3681
1.3636
1.3592
1.3548
1.3504
1.3460
1.3417
1.3374
1.3331
1.3288
1.3246
1.3204
1.3251
1.3206
1.3162
1.3120
1.3078
1.3037
1.2997
1.2956
1.2916
1.2876
1.2835
1.2795
1.2756
1.2716
1.2677
1.2637
1.2599
1.2510
1.2470
1.2431
1.2391
1.2352
1.2314
1.2277
1.2241
1.2204
1.2168
1.2132
1.2097
1.2061
1.2025
1.1990
1.1955
1.192
1.1684
1.1649
1.1614
1.1579
1.1543
1.1509
1.1476
1.1443
1.1410
1.1378
1.1346
1.1314
1.1283
1.1251
1.1220
1.1189
1.1157
Standard uncertainties u are u(T) = 0.02 K, u are u(x,y) = 0.0001, u(p) = 10 kPa, and the combined expanded uncertainty Uc is Uc(ρ) = 0.5 kg·m−3,
with expanded uncertainty at the 0.95 confidence level (k ≈ 2).
a
orders: [C4C1im][NTf2] > [C4C1im[CF3SO3] > [C4C1im][PF6] > [C4C1im][BF4] > [C4C1im][(CH3O)2PO2] > [C4C1im][CH3CO2]. However, the opposite trend is observed for the
density of cyano-based ILs; i.e., ILs with smaller anions in terms
of volume lead to denser ILs ([C4C1im][SCN] > [C4C1im][N(CN)2] > [C4C1im][C(CN)3]). As previously observed by
Neves et al.,40 the anions in this series are not completely
homologous due to the presence of different central atoms.
The temperature dependence of density for the mixtures of ILs
measured in this work is depicted in Figure 1 and reported in
Table 3. The same scale was used in the density plots for all
of the studied systems so that density variations can be better
appreciated. It can be seen that all systems show a linear
dependence of density with temperature, where the density
decreases with the increase of temperature. Since the pure
[C4C1im][NTf2] IL is present in all of the studied mixtures, and
taking into account that it has the highest density values among
the studied ILs, the decrease of the mole fraction of this IL leads
to a density decrease for all of the studied mixtures. Also, for the
systems where there is a large difference in density between the
two ILs constituents of the mixture, such as the case of [C4C1im][NTf2]x[SCN](1−x), [C4C1im][NTf2]x[N(CN)2](1−x), [C4C1im][NTf2]x[C(CN)3](1−x), [C4C1im][NTf2]x[CH3CO2](1−x), and
[C4C1im][NTf2]x[(CH3O)2PO2](1−x), the variation of density
along the mixture composition is thus more evident.
The density values (ρ) were fitted as a function of temperature,
T (K), by a least-squares method, using the linear expression
given by eq 1,
to 0.23%. In summary, the absolute average relative deviations
(AARD) between the data collected in this work for the density
values of pure ILs and those reported in the literature are
0.12%,18 0.05%,19,20 0.03%,21 and 0.01%,22 for [C4C1im][NTf2];
0.07%40 and 0.04%30 for [C4C1im][SCN]; 0.28%,26 0.08%,22
0.03%,31 and 0.01%40 for [C 4C 1im][N(CN)2]; 0.04%26
and 0.02%32,40 for [C4C1im][C(CN)3]; 0.07%,21 0.03%,33 and
0.01%34 for [C4C1im][BF4]; 0.04%,21 0.03%,20 and 0.02%35 for
[C 4 C 1 im][PF 6 ]; 0.20% 24 and 0.01% 36,37 for [C 4 C 1 im][CH3CO2]; 0.62%,34 0.25%,31 and 0.18%38 for [C4C1im][CF3SO3]; and 0.37%39 for [C4C1im][(CH3O)2PO2]. In
summary, no significant differences exist in the densities values
reported for the same set of ILs.
Regarding mixtures of ILs, Clough et al.11 also determined the
density of [C4C1im][NTf2]x[CF3SO3](1−x) and [C4C1im][NTf2]x[(CH3O)2PO2](1−x) at 298.15 K. For the pure fluids,
the density deviations are below 0.01%, while for [C4C1im][NTf2]x[CF3SO3](1−x) and [C4C1im][NTf2]x[(CH3O)2PO2](1−x) low negative deviations were also obtained.
In general, for a given temperature, the densities of the pure
ILs at a fixed temperature can be ordered according to the
following sequence: [C4C1im][NTf2] > [C4C1im][PF6] >
[C4C1im[CF3SO3] > [C4C1im][BF4] > [C4C1im][(CH3O)2PO2] > [C4C1im][SCN] > [C4C1im][N(CN)2] ≈ [C4C1im][CH3CO2] > [C4C1im][C(CN)3]. As expected, and with
few exceptions, the density data for ILs bearing the same
cation can be correlated with the anion size (see VM in
Table 2, since cation is constant in these mixtures, the effect
of the anion size is easily perceived): the smaller the anion
size, the smaller the density, according to the following
ρ = a + b(T )
2832
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DOI: 10.1021/acs.jced.6b00178
J. Chem. Eng. Data 2016, 61, 2828−2843
Journal of Chemical & Engineering Data
Article
Figure 1. Densities of IL mixtures and their temperature dependence: (A) [C4C1im][NTf2]x[SCN](1−x), (B) [C4C1im][NTf2]x[N(CN)2](1−x), (C)
[C4C1im][NTf2]x[C(CN)3](1−x), (D) [C4C1im][NTf2]x[BF4](1−x), (E) [C4C1im][NTf2]x[PF6](1−x), (F) [C4C1im][NTf2]x[CF3SO3](1−x), (G)
[C4C1im][NTf2]x[CH3CO2](1−x), and (H) [C4C1im][NTf2]x[(CH3O)2PO2](1−x); ⧫, x = 1.00; ■, x = 0.75; ▲, x = 0.50; ●, x = 0.25; , x = 0.00;
and respective correlation using the least-squares method by eq 1 (lines).
some controversy,41,42 the use of a linear function is enough to
describe the measured density data in this work, at least within
the temperature range studied. The fitting given by eq 1 is also
presented in Figure 1.
where a and b are adjustable parameters, presented in Table 4
together with the respective correlation coefficients.
Although the use of a linear correlation or a second-order
polynomial equation to correlate experimental density data raises
2833
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Article
Table 4. Fitted Parameters of eq 1a and Respective Correlation Coefficients, R2, and Thermal Expansion Coefficients, αp, and
Respective Standard Deviations (σ), for the Studied Pure ILs and Their Mixtures at 298.15 K and 0.1 MPa
[C4C1im][NTf2]
[C4C1im][SCN]
[C4C1im][N(CN)2]
[C4C1im][C(CN)3]
[C4C1im][BF4]
[C4C1im][PF6]
[C4C1im][CH3CO2]
[C4C1im][CF3SO3]
[C4C1im][(CH3O)2PO2]
[C4C1im][NTf2]0.25[SCN]0.75
[C4C1im][NTf2]0.50[SCN]0.50
[C4C1im][NTf2]0.75[SCN]0.25
[C4C1im][NTf2]0.25[N(CN)2]0.75
[C4C1im][NTf2]0.50[N(CN)2]0.50
[C4C1im][NTf2]0.75[N(CN)2]0.25
[C4C1im][NTf2]0.25[C(CN)3]0.75
[C4C1im][NTf2]0.50[C(CN)3]0.50
[C4C1im][NTf2]0.75[C(CN)3]0.25
[C4C1im][NTf2]0.25[BF4]0.75
[C4C1im][NTf2]0.50[BF4]0.50
[C4C1im][NTf2]0.75[BF4]0.25
[C4C1im][NTf2]0.25[PF6]0.75
[C4C1im][NTf2]0.50[PF6]0.50
[C4C1im][NTf2]0.75[PF6]0.25
[C4C1im][NTf2]0.25[CF3SO3]0.75
[C4C1im][NTf2]0.50[CF3SO3]0.50
[C4C1im][NTf2]0.75[CF3SO3]0.25
[C4C1im][NTf2]0.25[CH3CO2]0.75
[C4C1im][NTf2]0.50[CH3CO2]0.50
[C4C1im][NTf2]0.75[CH3CO2]0.25
[C4C1im][NTf2]0.25[(CH3O)2PO2]0.75
[C4C1im][NTf2]0.50[(CH3O)2PO2]0.50
[C4C1im][NTf2]0.75[(CH3O)2PO2]0.25
a
a (g·cm−3)
b × 104 (g·cm−3·K−1)
R2
104 (αp ± σ) (K−1)
1.7168
1.2426
1.2462
1.2458
1.4082
1.6112
1.2328
1.5280
1.3513
1.4022
1.5271
1.6322
1.3955
1.5024
1.6298
1.3880
1.5117
1.6203
1.5120
1.5938
1.6648
1.6427
1.6719
1.6943
1.5877
1.6337
1.6777
1.3955
1.5220
1.6308
1.4558
1.5520
1.6384
−9.38
−5.78
−6.24
−6.65
−6.94
−8.17
−6.04
−7.77
−6.50
−6.94
−7.85
−8.74
−7.13
−7.85
−8.78
−7.41
−8.15
−8.80
−7.81
−8.42
−9.04
−8.50
−8.86
−9.09
−8.32
−8.67
−9.05
−7.16
−8.00
−8.82
−7.28
−8.05
−8.77
0.9999
0.9998
0.9997
0.9998
0.9998
0.9998
0.9998
0.9996
0.9999
0.9995
0.9995
0.9998
0.9998
0.9998
0.9999
0.9998
0.9998
0.9998
0.9998
0.9998
0.9998
0.9998
0.9999
0.9998
0.9999
0.9999
0.9999
0.9999
0.9999
0.9999
0.9999
0.9999
0.9999
6.65 ± 0.11
5.46 ± 0.08
5.95 ± 0.09
6.44 ± 0.10
5.88 ± 0.09
6.04 ± 0.09
5.85 ± 0.09
6.09 ± 0.09
5.75 ± 0.08
5.90 ± 0.09
6.17 ± 0.10
6.46 ± 0.11
6.14 ± 0.10
6.29 ± 0.10
6.52 ± 0.11
6.48 ± 0.11
6.54 ± 0.11
6.60 ± 0.11
6.14 ± 0.10
6.36 ± 0.10
6.52 ± 0.11
6.22 ± 0.10
6.39 ± 0.10
6.53 ± 0.11
6.32 ± 0.10
6.43 ± 0.10
6.53 ± 0.11
6.17 ± 0.10
6.39 ± 0.10
6.56 ± 0.11
6.02 ± 0.09
6.28 ± 0.10
6.48 ± 0.11
Standard uncertainties u are u(a) = 0.002 and u(b) = 4 × 10−6.
The molar volumes of both pure ILs and their mixtures, at
298.15 K, are depicted in Figure 2, and listed in Table S1 in the
Supporting Information. Straight lines connecting the pure fluid
density values represent the ideal molar volume, which is also
listed in Table 5 for each one of the studied compositions. The
molar volume of a mixture is directly related to the chemical
potentials of the pure compounds present in the mixture and
thus displays a linear dependence with the mole fraction when
ideal mixing occurs. As expected, very small deviations from the
ideal behavior can be generally observed for all of the most of
the studied mixtures, with the highest deviation found for the
[C4C1im][NTf2]0.5[N(CN)2]0.5 mixture. It should be noted that
the differences between the experimental and the ideal molar
volumes for the ILs mixtures are in general very small (tenths of
the unit) in comparison to the molar volumes (in order of
hundreds of the unit) used in their calculations. In order to better
appreciate the very small deviations of the experimental molar
volumes from the ideality, the excess molar volumes were also
calculated using Equation 4 and are listed in Table 5 and depicted
in Figure S2, in Supporting Information.
The thermal expansion coefficient values at a given pressure
were calculated for both the pure and the IL mixtures using the
following equation:
αP = −
⎛ ∂ ln ρ ⎞
1 ⎛ ∂ρ ⎞
⎜
⎟ = ⎜
⎟
⎝
⎠
ρ ∂T P ⎝ ∂T ⎠ P
(2)
where ρ is the density in g·cm−3, T is the temperature in K, and P
is the pressure in kPa.
The thermal expansion coefficient values of all of the studied
pure and mixtures of ILs are provided in Table 4. Since the
thermal expansion coefficients obtained in this work for the pure
ILs and their binary mixture in the temperature range from
283.15 to 363.15 K and 0.1 MPa do not change considerably with
temperature, in accordance to what was observed in the
literature,41,43 an average thermal expansion coefficient independent of temperature is here provided.
The molar volumes (Vm) of the pure ILs and their mixtures
were calculated applying eq 3,
Vm,exp =
x1M1 + x 2M 2
ρ
(3)
⎛x M
xM ⎞
Vm = Vm,exp − ⎜⎜ 1 1 + 2 2 ⎟⎟
ρ2 ⎠
⎝ ρ1
where x is the mole fraction and M is the molecular weight
(g·mol−1). The subscripts 1 and 2 refer to each pure IL.
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Article
Figure 2. Molar volumes of the studied mixtures: (A) [C4C1im][NTf2]x[SCN](1−x), (B) [C4C1im][NTf2]x[N(CN)2](1−x), (C) [C4C1im][NTf2]x[C(CN)3] (1−x) , (D) [C4C1 im][NTf 2]x[BF4](1−x) , (E) [C4C1 im][NTf 2]x[PF6](1−x) , (F) [C4C1im][NTf2] x[CF3 SO3](1−x), (G) [C4C1im][NTf2]x[CH3CO2](1−x), and (H) [C4C1im][NTf2]x[(CH3O)2PO2](1−x), at 298.15 K and 0.1 MPa. Blue diamond represents experimental molar
volume; straight lines and red circles represent the ideal behavior described by eq 3.
where Vm,exp corresponds to the molar volume of the mixture and
the second term corresponds to the ideal molar volume of the
mixture.
The most striking feature of the excess molar volume representation is that the small experimental error in density is directly
translated in considerable error in the excess molar volumes, due
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Table 5. Experimental Molar Volume (Vm,exp), Ideal Molar Volume (Vm,id), and Excess Molar Volume (VE) for Pure ILs and Their
Mixtures at T = 298.15 K and 0.1 MPa
x [C4C1im][NTf2] + (1 − x) [C4C1im][SCN]
x
1.0000
0.7483
0.4999
0.2501
0.0000
x
1.0000
0.7508
0.4999
0.2517
0.0000
x
1.0000
0.7479
0.4996
0.2499
0.0000
−3
ρ (g·cm )
−1
Vm,exp (cm ·mol )
3
−1
Vm,id (cm ·mol )
3
1.4372
291.80
291.80
1.3717
264.75
264.46
1.2931
238.40
238.03
1.1954
211.25
210.93
1.0702
184.36
184.36
x [C4C1im][NTf2] + (1 − x) [C4C1im][C(CN)3]
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
1.4372
291.80
291.80
1.3581
274.33
274.17
1.2688
255.56
255.28
1.1672
237.92
237.77
1.0476
218.86
218.86
x [C4C1im][NTf2] + (1 − x) [C4C1im][PF6]
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
1.4372
291.80
291.80
1.4237
270.71
270.71
1.408
250.70
250.69
1.3894
230.01
229.97
1.3676
209.99
209.99
x [C4C1im][NTf2] + (1 − x) [C4C1im][CH3CO2]
x [C4C1im][NTf2] + (1-x) [C4C1im][N(CN)2]
−1
V (cm ·mol )
x
0.00
0.29
0.37
0.32
0.00
1.0000
0.7486
0.4569
0.2506
0.0000
VE (cm3·mol−1)
x
0.00
0.16
0.28
0.15
0.00
1.0000
0.7509
0.4979
0.2497
0.0000
VE (cm3·mol−1)
x
0.00
0.00
0.01
0.04
0.00
1.0000
0.7460
0.5001
0.2503
0.0000
E
3
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
VE (cm3·mol−1)
1.4372
291.80
291.80
1.3681
267.07
266.96
1.2685
246.21
245.41
1.183
218.73
218.06
1.0602
193.60
193.60
x [C4C1im][NTf2] + (1 − x) [C4C1im][BF4]
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
0.00
0.11
0.80
0.67
0.00
VE (cm3·mol−1)
1.4372
291.80
291.80
1.3951
266.18
266.08
1.3428
239.31
238.94
1.2791
214.55
214.11
1.2016
188.10
188.10
x [C4C1im][NTf2] + (1-x) [C4C1im][CF3SO3]
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
0.00
0.10
0.37
0.44
0.00
VE (cm3·mol−1)
1.4372
291.80
291.80
1.4078
273.48
273.35
1.3755
257.29
257.15
1.3398
238.87
238.95
1.2963
222.39
222.39
x [C4C1im][NTf2] + (1 − x) [C4C1im][(CH3O)2PO2]
0.00
0.13
0.14
−0.08
0.00
x
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
VE (cm3·mol−1)
x
ρ (g·cm−3)
Vm,exp (cm3·mol−1)
Vm,id (cm3·mol−1)
VE (cm3·mol−1)
1.0000
0.7487
0.4984
0.2498
0.0000
1.4372
1.3678
1.2838
1.1819
1.0528
291.80
265.76
239.78
214.23
188.32
291.80
265.51
239.29
213.88
188.32
0.00
0.25
0.49
0.35
0.00
1.0000
0.7468
0.5005
0.2499
0.0000
1.4372
1.377
1.312
1.2391
1.1579
291.80
275.36
260.70
243.71
228.03
291.80
274.90
260.17
243.21
228.03
0.00
0.46
0.53
0.50
0.00
to their very small values. Thus, the accuracy of density measurements is a crucial factor when discussing excess molar
volumes and the information derived from these results.
Viscosity-Derived Properties. The viscosity of pure ILs
and mixtures of ILs were measured at 0.1 MPa in the temperature
range from 283.15 to 363.15 K and are presented in Table 6.
Contrarily to density values discussed before, viscosities for
pure ILs display considerable discrepancies among different
authors.20,21,23−26,31,33,39−41,44−48 The absolute average relative
deviations between the data collected in this work and those
reported in the literature are 2.98%,23 2.91%,24 2.57%,20 0.96%,21
and 0.12%25 for [C4C1im][NTf2]; 9.52%40 for [C4C1im][SCN];
3.28%,26 0.84%,31 and 0.60%40 for [C4C1im][N(CN)2]; 3.62%26
and 0.54%40 for [C4C1im][C(CN)3]; 3.80%,44 2.16%,21 and
0.98%33 for [C4C1im][BF4]; 3.17%,21 2.98%,45 and 0.08%46 for
[C4C1im][PF6]; 34.75%,36 33.49%,47 and 1.17%41 for [C4C1im][CH3CO2]; 16.90%48 and 10.59%31 for [C4C1im][CF3SO3];
and 8.36%39 for [C4C1im][(CH3O)2PO2]. The average relative
deviations between the data collected in this work and those
already reported in literature20,21,23−26,31,33,39−41,44−48 are
depicted in Figure S3. It is well-known that the viscosity of ILs
is highly affected by the presence of small amounts of impurities.
One of the main reason for the high viscosity variations of
[C4C1im][CH3CO2] is due to the source where ILs are purchased, where differences of the purity and purification procedures may cause a wide variation between the viscosity results in
this work and those previously reported. In addition, the measurement technique, the sample purification steps, and the
sample handling are also additional factors that may lead to large
divergences in the viscosity values.49
Regarding the viscosity of mixtures of ILs, the results obtained
in this work show a similar behavior to those presented by
Clough et al.11 for the systems [C4C1im][NTf2]x[CF3SO3](1−x)
and [C4C1im][NTf2]x[(CH3O)2PO2](1−x). Since Clough et al.11
prepared mixtures with different mole fractions, it is not possible
to calculate direct deviations.
For a given temperature, the viscosity of pure ILs, for instance
at 298.15 K, decreases according to the following trend:
[C4C1im][(CH3O)2PO2] > [C4C1im][CH3CO2] > [C4C1im][PF6] > [C4C1im][BF4] > [C4C1im][CF3SO3] > [C4C1im][SCN] > [C4C1im][NTf2] > [C4C1im][N(CN)2] ≈ [C4C1im][C(CN)3]. Two factors might be playing a major role in this
trend: size or entanglement of the ions and/or the establishment
of strong interactions between the different ions. The most
viscous ILs here studied are those containing nonfluorinated
organic acids derived anions, known for their capacity to establish
strong hydrogen bonds with other ions,50 thus explaining their
high viscosity. Within this family, [C4C1im][(CH3O)2PO2] has
also a larger molar volume which explains its higher viscosity.
The ILs with intermediate viscosity are those bearing fluorine
anions, with the exception [C4C1im][PF6] which displays high
viscosity, due to the large cation−anion interactions.29 The most
fluid ILs are those containing cyano groups. However, the less
viscous liquids in this family are also the bulkier ones, in contrast
to what happens to the previous two families of ILs. This
behavior was previously discussed by Neves et al.,40 and it was
related to the intermolecular interactions that occur at the bulk
liquid.
The viscosity values for the pure and mixtures of ILs studied in
this work are depicted in Figure 3 and reported in Table 6. For all
systems, the viscosity decreases with the increase in temperature,
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Article
Table 6. Experimental Dynamic Viscosities (η) of [C4mim][NTf2]x[Y]y IL Mixtures on Mole Fraction (x1) as a Function of
Temperature (T) at Pressure p = 0.1 MPaa
x [C4C1im][NTf2] + (1 − x) [C4C1im][SCN]
x [C4C1im][NTf2] + (1 − x) [C4C1im][N(CN)2]
η (mPa·s)
η (mPa·s)
x
T (K)
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
T (K)
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.000
0.748
0.500
x
0.250
106.78
115.12
124.13
133.49
82.142
88.289
94.681
101.08
66.356
71.221
76.166
80.920
51.580
55.058
58.499
61.694
41.940
44.621
47.235
49.547
34.601
36.704
38.704
40.423
29.479
31.225
32.846
34.219
24.472
25.811
27.027
28.045
20.928
22.012
22.975
23.786
18.071
18.956
19.740
20.387
15.947
16.702
17.356
17.910
13.828
14.436
14.940
15.384
12.234
12.744
13.160
13.539
10.898
11.328
11.671
11.998
9.9850
10.359
10.653
10.916
8.8060
9.1135
9.3505
9.5766
7.9803
8.2417
8.4395
8.6206
x [C4C1im][NTf2] + (1 − x) [C4C1im][C(CN)3]
1.000
0.000
T (K)
139.54
104.51
82.913
62.635
49.936
40.483
34.081
27.804
23.489
20.064
17.577
15.077
13.238
11.713
10.672
9.3553
8.4365
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.000
0.749
0.457
106.77
95.811
82.163
73.993
64.531
58.315
51.601
46.816
41.933
38.184
34.585
31.605
28.907
26.501
24.456
22.481
20.908
19.273
18.052
16.681
15.719
14.564
13.797
12.817
12.198
11.360
10.856
10.136
9.7200
9.0975
8.7541
8.2106
7.9257
7.4488
x [C4C1im][NTf2] + (1 −
η (mPa·s)
η (mPa·s)
x
x
0.751
0.501
106.77
88.875
82.163
68.485
64.531
53.860
51.601
43.148
41.933
35.156
34.585
29.072
28.907
24.374
24.456
20.684
20.908
17.745
18.052
15.384
15.719
13.437
13.797
11.837
12.198
10.504
10.856
9.387
9.7200
8.4352
8.7541
7.6234
7.9257
6.9255
x [C4C1im][NTf2] + (1
0.252
77.278
65.872
59.443
50.602
46.775
39.793
37.605
31.918
30.660
26.075
25.433
21.650
21.394
18.218
18.216
15.530
15.719
13.389
13.614
11.663
11.899
10.249
10.543
9.0781
9.3836
8.0998
8.4227
7.2747
7.5491
6.5736
6.8579
5.9737
6.2877
5.4554
− x) [C4C1im][PF6]
0.000
T (K)
58.153
44.500
34.896
27.974
22.854
18.979
15.995
13.657
11.796
10.291
9.0624
8.0449
7.1942
6.4748
5.8619
5.3373
4.8837
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1.000
0.751
0.251
82.502
72.335
64.112
56.465
50.832
44.977
41.019
36.451
33.660
30.024
28.006
25.081
23.603
21.219
20.116
18.156
17.327
15.700
15.056
13.693
13.267
12.047
11.723
10.676
10.432
9.5297
9.3349
8.560
8.4083
7.7277
7.6155
7.0165
6.9321
6.4030
x) [C4C1im][BF4]
0.498
0.250
106.77
127.96
158.06
200.83
82.163
97.869
119.67
149.79
64.531
76.327
92.467
114.12
51.601
60.641
72.767
88.561
41.933
48.975
58.236
69.908
34.585
40.138
47.312
56.119
28.907
33.348
38.961
45.704
24.456
28.045
32.485
37.722
20.908
23.853
27.356
31.518
18.052
20.484
23.288
26.630
15.719
17.751
20.023
22.707
13.797
15.514
17.365
19.581
12.198
13.660
15.186
17.022
10.856
12.112
13.383
14.910
9.7200
10.807
11.844
13.146
8.7541
9.6882
10.551
11.663
7.9257
8.7334
9.4667
10.420
x [C4C1im][NTf2] + (1 − x) [C4C1im][CH3CO2]
η (mPa·s)
η (mPa·s)
x
x
0.000
58.350
45.906
36.830
30.080
24.945
20.979
17.865
15.383
13.384
11.739
10.383
9.2509
8.2978
7.4878
6.7943
6.1965
5.6772
0.000
264.99
192.43
143.08
108.74
84.284
66.520
53.372
43.471
35.894
30.014
25.376
21.683
18.696
16.263
14.256
12.591
11.196
T (K)
1.000
0.748
0.500
0.250
0.000
T (K)
1.000
0.749
0.498
0.250
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
106.77
82.163
64.531
51.601
41.933
34.585
28.907
24.456
20.908
18.052
15.719
13.797
148.25
112.57
87.233
68.875
55.303
45.077
37.247
31.165
26.376
22.556
19.471
16.955
221.31
166.04
126.16
97.744
77.094
61.820
50.313
41.516
34.680
29.299
25.002
21.534
360.25
264.71
196.39
148.96
115.08
90.440
72.177
58.449
47.959
39.841
33.466
28.386
794.33
557.27
393.86
285.02
210.93
159.46
122.78
96.281
76.721
62.044
50.855
42.201
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
106.78
82.142
66.356
51.580
41.940
34.601
29.479
24.472
20.928
18.071
15.947
13.828
175.10
129.87
101.85
76.324
60.267
48.439
40.339
32.702
27.359
23.178
20.113
17.145
310.72
220.24
159.18
119.72
91.377
71.140
56.475
45.443
37.162
30.802
26.092
21.927
577.38
385.58
265.43
189.58
138.72
104.00
79.571
62.278
49.567
40.094
33.138
27.382
1013.40
645.60
421.35
292.57
206.68
150.08
110.79
85.027
66.071
52.293
42.287
34.385
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Journal of Chemical & Engineering Data
Article
Table 6. continued
x [C4C1im][NTf2] + (1 − x) [C4C1im][PF6]
x [C4C1im][NTf2] + (1 − x) [C4C1im][CH3CO2]
η (mPa·s)
η (mPa·s)
x
T (K)
1.000
343.15
348.15
353.15
358.15
363.15
12.198
14.880
10.856
13.148
9.7200
11.698
8.7541
10.473
7.9257
9.4276
x [C4C1im][NTf2] + (1 −
0.748
0.500
x
0.250
18.705
24.305
16.376
20.992
14.442
18.288
12.824
16.042
11.455
14.168
x) [C4C1im][CF3SO3]
0.000
T (K)
35.427
30.038
25.722
22.222
19.363
343.15
348.15
353.15
358.15
363.15
1.000
0.749
0.498
12.234
14.955
10.898
13.127
9.9850
11.891
8.8060
10.347
7.9803
9.2719
x [C4C1im][NTf2] + (1 − x)
η (mPa·s)
0.250
18.788
23.054
16.247
19.626
14.490
17.208
12.454
14.643
11.024
12.813
[C4C1im][(CH3O)2PO2]
0.000
28.476
23.878
20.631
17.348
15.003
η (mPa·s)
x
x
T (K)
1.000
0.746
0.500
0.250
0.000
T (K)
1.000
0.747
0.501
0.250
0.000
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
106.78
82.142
66.356
51.580
41.940
34.601
29.479
24.472
20.928
18.071
15.947
13.828
12.234
10.898
9.9850
8.8060
7.9803
145.79
111.50
87.296
68.684
55.861
45.795
38.101
32.200
27.440
23.466
20.273
17.604
15.457
13.662
12.227
10.929
9.9093
145.00
109.34
84.529
66.622
53.393
43.559
35.960
30.150
25.432
21.659
18.550
16.080
14.132
12.541
11.183
9.9806
8.9726
154.70
117.06
90.691
71.417
57.294
46.662
38.523
32.190
27.212
23.236
20.057
17.397
15.234
13.429
11.944
10.634
9.5407
225.61
168.05
128.51
99.144
78.260
62.755
51.328
42.099
35.127
29.632
25.498
21.720
18.840
16.474
14.834
12.864
11.476
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
106.78
82.142
66.356
51.580
41.940
34.601
29.479
24.472
20.928
18.071
15.947
13.828
12.234
10.898
9.9850
8.8060
7.9803
251.51
183.60
137.30
104.86
81.713
64.812
52.462
42.722
35.402
29.688
25.420
21.556
18.628
16.232
14.572
12.605
11.217
630.61
433.30
301.49
222.26
165.15
125.35
96.268
76.392
61.136
49.652
41.066
34.048
28.686
24.417
21.362
18.178
15.879
1433.70
930.25
618.01
432.55
307.85
224.53
166.25
127.53
98.918
78.040
62.705
50.834
41.865
34.896
29.799
25.026
21.499
2315.60
1454.60
943.97
641.71
446.92
319.33
232.10
174.70
133.37
103.62
81.972
65.623
53.395
44.013
37.081
30.935
26.332
a
Standard uncertainties u are u(T) = 0.02 K, u are u(x,y) = 0.0001, u(p) = 10 kPa, and the combined expanded uncertainty Ur is Ur(η) = 0.05, with
expanded uncertainty at the 0.95 confidence level (k ≈ 2).
model, described in eq 5,
and the viscosity values for the mixtures are between those of the
pure ILs. Unlike densities, viscosities do not vary linearly with the
IL mole fraction of a mixture, even for the mixtures where linear
volumetric behavior occurs. For the systems containing a second
IL that is more viscous than [C4C1im][NTf2], the viscosities
decrease with the addition of [C4C1im][NTf2], according to the
pure IL viscosity trend (Table 2) [C 4 C 1 im][NTf 2 ] x [(CH3O)2PO2](1−x) > [C4C1im][NTf2]x[CH3CO2](1−x) >
[C4C1im][NTf2]x[PF6](1−x) > [C4C1im][NTf2]x[BF4](1−x) >
[C4C1im][NTf2]x[SCN](1−x). For the systems containing a
second IL that is less viscous than [C4C1im][NTf2], the viscosities increase with the addition of [C4C1im][NTf2], according to
the pure IL viscosity trend (Table 2): [C4C1im][NTf2]x[N(CN)2](1−x) < [C4C1im][NTf2]x[C(CN)3](1−x). However, an
odd behavior was observed for the [C4C1im][NTf2]x[CF3SO3](1−x) system. Since the viscosity of [C4C1im][CF3SO3] is higher than that of [C4C1im][NTf2], the addition of
this last IL should always decrease the viscosity of the mixture.
Nevertheless, the viscosities for this system decrease according to
the following mole fraction sequence: x = 0.00 > 0.25 > 0.50 ≈
0.75 > 1.00. This might be due to the similar molecular structure
of the two anions present in the mixture, where it can be assumed
that [CF3SO3]− is “half” of [NTf2]−.
The experimental viscosity values were fitted as a function of
temperature, using the Vogel−Fulcher−Tammann (VTF)
ln η = A η +
Bη
(T − Cη)
(5)
where η is the viscosity in mPa·s, T is the temperature in K, and
Aη (mPa·s), Bη (K), and Cη (K) are adjustable parameters. The
adjustable parameters were determined from the fitting of the
experimental data and are presented along with the absolute
average relative deviation (ARD) in Table 7.
The absolute average relative deviation was calculated
according to eq 6
ARD(%) =
1
N
N
∑
i=1
ηcalc, i − ηexp, i
ηexp, i
× 100
(6)
where N is the total number of experimental points and ηexp and
ηcalc are the experimental and calculated viscosity, respectively.
The fitting of the viscosity data as a function of temperature is
also depicted in Figure 3.
The energy barrier was determined through eq 7, based on the
viscosity dependence with temperature,
⎛
⎞
⎜
⎟
Bη
∂ln η
⎜
⎟
=
Eη = R ×
R
1
⎞⎟
2C η
⎜ ⎛⎜ Cη2
∂ T
⎜ 2 − T + 1⎟ ⎟
⎠⎠
⎝ ⎝T
()
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Figure 3. Viscosities of IL mixtures and their temperature dependence: (A) [C4C1im][NTf2]x[SCN](1−x), (B) [C4C1im][NTf2]x[N(CN)2](1−x), (C)
[C4C1im][NTf2]x[C(CN)3](1−x), (D) [C4C1im][NTf2]x[BF4](1−x), (E) [C4C1im][NTf2]x[PF6](1−x), (F) [C4C1im][NTf2]x[CF3SO3](1−x), (G)
[C4C1im][NTf2]x[CH3CO2](1−x), and (H) [C4C1im][NTf2]x[(CH3O)2PO2](1−x); ⧫, x = 1.00; ■, x = 0.75; ▲, x = 0.50; ●, x = 0.25; , x = 0.00,
and respective correlation using eq 4 (lines).
where η, T, Bη, and Cη were obtained from eq 5, and R is the
universal gas constant (8.3144598 × 10−3 kJ·K−1·mol−1). The
energy barrier of a fluid to share stress at 298.15 K is listed in
Table 7 and depicted in Figure 4. Eη is the energy barrier that
must be overcome to move ions upon the other ions in the IL.
Therefore, the higher the Eη value is, the more difficult it is for the
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Table 7. Fitted Parameters of eq 4, Respective AARD, and Energy Barriers (Eη) Values at T = 298.15 K and 0.1 MPa
[C4C1im][NTf2]
[C4C1im][SCN]
[C4C1im][N(CN)2]
[C4C1im][C(CN)3]
[C4C1im][BF4]
[C4C1im][PF6]
[C4C1im][CH3CO2]
[C4C1im][CF3SO3]
[C4C1im][(CH3O)2PO2]
[C4C1im][NTf2]0.25[SCN]0.75
[C4C1im][NTf2]0.50[SCN]0.50
[C4C1im][NTf2]0.75[SCN]0.25
[C4C1im][NTf2]0.25[N(CN)2]0.75
[C4C1im][NTf2]0.50[N(CN)2]0.50
[C4C1im][NTf2]0.75[N(CN)2]0.25
[C4C1im][NTf2]0.25[C(CN)3]0.75
[C4C1im][NTf2]0.75[C(CN)3]0.25
[C4C1im][NTf2]0.50[C(CN)3]0.50
[C4C1im][NTf2]0.25[BF4]0.75
[C4C1im][NTf2]0.50[BF4]0.50
[C4C1im][NTf2]0.75[BF4]0.25
[C4C1im][NTf2]0.25[PF6]0.75
[C4C1im][NTf2]0.50[PF6]0.50
[C4C1im][NTf2]0.75[PF6]0.25
[C4C1im][NTf2]0.25[CF3SO3]0.75
[C4C1im][NTf2]0.50[CF3SO3]0.50
[C4C1im][NTf2]0.75[CF3SO3]0.25
[C4C1im][NTf2]0.25[CH3CO2]0.75
[C4C1im][NTf2]0.50[CH3CO2]0.50
[C4C1im][NTf2]0.75[CH3CO2]0.25
[C4C1im][NTf2]0.25[(CH3O)2PO2]0.75
[C4C1im][NTf2]0.50[(CH3O)2PO2]0.50
[C4C1im][NTf2]0.75[(CH3O)2PO2]0.25
Aη (mPa·s)
Bη (K)
Cη (K)
AARD (%)
Eη(298.15 K) (kJ·mol−1)
−8.8750
−8.9508
−9.0543
−9.3007
−8.8467
−8.5595
−9.0081
−8.7108
−8.6896
−8.8761
−8.8694
−8.8652
−8.9897
−8.9359
−8.9155
−9.2077
−8.9899
−9.0721
−8.8069
−8.8172
−8.8278
−8.7959
−8.8510
−8.7944
−8.9314
−8.9942
−8.7078
−9.1858
−9.0904
−8.9149
−8.7835
−8.8557
−8.8055
823.398
824.105
821.843
822.517
825.308
826.324
826.860
825.309
869.013
823.929
823.810
823.688
823.020
823.168
823.424
823.099
823.393
823.268
824.560
824.215
823.691
870.393
865.923
823.869
869.592
865.568
823.705
871.269
866.643
824.273
868.111
867.343
824.751
159.006
165.008
150.080
154.458
173.596
184.962
191.673
169.189
192.484
163.014
161.646
160.209
153.200
154.794
157.489
155.328
157.321
155.999
168.958
165.136
161.438
171.856
165.420
163.497
159.955
160.466
161.698
182.287
173.746
168.227
188.586
179.994
172.218
0.80
1.00
1.01
1.01
0.21
1.57
0.70
0.57
1.71
0.83
0.72
0.75
0.79
0.73
0.48
1.33
0.72
0.97
0.30
0.26
0.19
0.78
0.13
0.09
0.14
0.33
0.29
0.37
0.34
0.66
1.50
0.72
0.38
31.43
34.36
27.70
27.70
39.32
47.67
53.90
36.68
57.53
33.35
32.68
31.99
28.95
29.60
30.76
28.95
30.69
30.11
36.51
34.43
32.57
40.33
36.33
33.58
33.65
33.75
32.70
47.97
41.39
36.09
53.45
45.92
38.44
ions to move past each other. This can be a direct effect of the size
or entanglement of the ions and/or by the presence of stronger
interactions in the fluid. From the analysis of Figure 4, only the
pure [C4C1im][N(CN)2] and [C4C1im][C(CN)3] ILs and
the systems containing these two ILs, [C4C1im][N(CN)2]x[NTf2](1−x) and [C4C1im][C(CN)3]x[NTf2](1−x), present lower
Eη than the pure [C4C1im][NTf2], while the other pure ILs and
their mixtures with [C4C1im][NTf2] present higher Eη values.
Also to be noted the almost constant values for the energy barrier
for [C4C1im][NTf2]x[CF3SO3](1−x), due to the similarity
between both ILs as discussed before.
The viscosity of IL mixtures can be calculated from the pure IL
viscosities using the ideal Grunberg and Nissan mixing rules,51
according to the following equation
log10(η) = x1 log10(η1) + x 2 log10(η2)
(8)
Figure 4. Energy barrier (Eη) for the mixtures studied at 298.15 K:
red ●, [C4C1im][(CH3O)2PO2]; orange ◆, [C4C1im][CH3CO2];
yellow ■, [C4C1im][PF6]; green ▲, [C4C1im][BF4]; blue ●,
[C4C1im[CF3SO3]; purple ◆, [C4C1im][SCN]; gray ■, [C4C1im][N(CN)2]; △, [C4C1im][C(CN)3]; ×, [C4C1im][NTf2].
The obtained results are compared in Figure 5 to the
experimental viscosity data (symbols) measured in this work for
all the systems studied, in the temperature range from 283.15
to 363.15 K. Surprisingly, it can be observed that, despite the
chemical and size differences (see VM in Table 2) between the
two ILs, the [C4C1im][NTf2]x[CH3CO2](1−x) system exhibits
very small deviations from the ideal Grunberg and Nissan mixing
rules. 5 1 For [C 4 C 1 im][NTf 2 ] x [BF 4 ] ( 1 − x ) , [C 4 C 1 im][NTf2 ]x[SCN](1−x) , [C 4C 1im][NTf2 ]x[N(CN)2](1−x) , and
[C4C1im][NTf2]x[C(CN)3](1−x) systems, small deviations are
observed, especially at lower temperatures. However, for the
[C4C1im][NTf2]x[(CH3O)2PO2](1−x) and [C4C1im][NTf2]x[PF6](1−x) systems, larger deviations are observed at lower
temperatures and lower mole fractions of [C4C1im][NTf2] (for
instance at x = 0.25). Larger deviations from ideality for the
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Figure 5. Viscosities for all the systems studied in this work: (A) [C4C1im][NTf2]x[SCN]y, (B) [C4C1im][NTf2]x[N(CN)2](1−x), (C) [C4C1im][NTf2]
x[C(CN)3](1−x), (D) [C4C1im][NTf2]x[BF4](1−x), (E) [C4C1im][NTf2 ]x[PF6](1−x), (F) [C4C1im][NTf2]x[CF3SO3](1−x), (G), [C4C1im][NTf2]x[CH3CO2](1−x), and (H) [C4C1im][NTf2]x[(CH3O)2PO2](1−x); red ◆, 283.15 K; orange ◆, 293.15 K; yellow ▲, 303.15 K; green ▲,
313.15 K; blue ■, 323.15 K; purple ■, 333.15 K; ○, 343.15 K; gray ●, 353.15 K; , 363.15 K, and description by the Grunberg and Nissan mixing rule51
(lines).
[C4C1im][NTf2]x[(CH3O)2PO2](1−x) mixture were also observed by Niedermeyer et al.9 As expected, the ideal Grunberg
and Nissan mixing rules51 fail in describing the viscosity of the
[C4C1im][NTf2]x[CF3SO3](1−x) system, due to the almost constant behavior of viscosity with the composition of the second IL.
Although Niedermeyer et al.9 supported the ideal/nonideal
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appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. H.F.D.A. acknowledges FCT for the PhD grant
SFRH/BD/88369/2012 and I.M.M. for a contract under the
program FCT Researcher 2012.
behavior according to the differences in polarity or hydrogenbonding ability (comprising both the basicity and acidity of the
IL ions) of each IL in the mixture, among other factors, our data
for [C4C1im][NTf2]x[CH3CO2](1−x) follow an opposite trend.
Both ILs are almost in the extremes of hydrogen-bond basicity
([NTf2]− versus [CH3CO2]−)50 and the mixture [C4C1im][NTf2]x[CH3CO2](1−x) follows an almost ideal behavior. Additionally, the two ILs in [C4C1im][NTf2]x[PF6](1−x) are composed of anions with similar hydrogen-bond basicity,50 and
larger deviations on their ideal mixing behavior were observed.
Therefore, even that substantial differences in hydrogen bonding
abilities might contribute to the observed deviations from ideality
these are not the dominant factor, and other factors do appear to
be critical as well as explained by the authors.9
■
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■
CONCLUSIONS
New experimental data were reported for density and dynamic
viscosity of eight mixtures of ILs in the temperature range
between 283.15 and 363.15 K and at 0.1 MPa. [C4C1im][NTf2]x[Y](1−x) mixtures were investigated, where [Y] covers
eight ILs with different anions and x covers five different mole
fractions, including pure ILs. The second IL was chosen in order
to evaluate the effect of distinct anions on the thermophysical
properties of IL mixtures and if these mixtures follow an ideal
behavior. In general, small deviations from ideality were observed
for density, while larger deviations were observed for viscosity for
some particular mixtures.
The mixing of ILs could potentially lead to fluids with
“tailored” properties within those displayed by the pure components. If mixtures of ILs follow a closely ideal behavior, it will
allow the prediction of their properties and their a priori finetuning. As shown in this work, and although some additional care
should be taken into account with some mixtures of ILs where
higher deviations from the ideal behavior were observed, in
general, ideal mixture models can be used to predict the physical
properties of IL mixtures.
■
ASSOCIATED CONTENT
* Supporting Information
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jced.6b00178.
Calculated molar volumes for the studied mixtures as a
function of composition and temperature and the relative
deviations between the experimental data and literature
data for density and viscosity for pure ILs; the excess molar
volumes and their standard deviations for the studied
mixtures (PDF)
■
REFERENCES
AUTHOR INFORMATION
Corresponding Author
*Tel.: +351-214469720. Fax: +351-214411277. E-mail address:
[email protected].
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
This work was funded by Fundaçaõ para a Ciencia e Tecnologia
(FCT) through PTDC/EQU-FTT/1686/2012, Research Unit
GREEN-it “Bioresources for Sustainability” (UID/Multi/
04551/2013), and POCI-01-0145-FEDER-007679 (FCT ref.
UID/CTM/50011/2013), CICECO-Aveiro Institute of Materials, financed by national funds through the FCT/MEC and when
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DOI: 10.1021/acs.jced.6b00178
J. Chem. Eng. Data 2016, 61, 2828−2843